Process for nano-scaled graphene plates

ABSTRACT

A process for producing a nano-scaled graphene plate. The material comprises a sheet of graphite plane or a multiplicity of sheets of graphite plane. The graphite plane is composed of a two-dimensional hexagonal lattice of carbon atoms and the plate has a length and a width parallel to the graphite plane and a thickness orthogonal to the graphite plane with at least one of the length, width, and thickness values being 100 nanometers or smaller. The process for producing nano-scaled graphene plate material comprises the steps of: a). partially or fully carbonizing a precursor polymer or heat-treating petroleum or coal tar pitch to produce a polymeric carbon containing micron- and/or nanometer-scaled graphite crystallites with each crystallite comprising one sheet or a multiplicity of sheets of graphite plane; b). exfoliating the graphite crystallites in the polymeric carbon; and c). subjecting the polymeric carbon containing exfoliated graphite crystallites to a mechanical attrition treatment to produce the nano-scaled graphene plate material.

This is a divisional application from a prior application Ser. No.10/274,473 (filing date Oct. 21, 2002).

FIELD OF THE INVENTION

The present invention relates to a nano-scaled thin-plate carbonmaterial, hereinafter referred to as nano-scaled graphene plate (NGP),and a process for producing the NGP material.

BACKGROUND

Carbon is known to have four unique crystalline structures, includingdiamond, graphite, fullerene and carbon nano-tubes. The carbon nano-tuberefers to a tubular structure grown with a single wall or multi-wall,which can be conceptually obtained by rolling up a graphite sheet (asheet of graphene plane or basal plane) or several graphite sheets toform a concentric hollow structure. A graphene plane is characterized byhaving a network of carbon atoms occupying a two-dimensional hexagonallattice. Carbon nano-tubes have a diameter on the order of a fewnanometers to a few hundred nanometers.

Carbon nano-tubes can function as either a conductor or a semiconductor,depending on the rolled shape and the diameter of the helical tubes. Itslongitudinal, hollow structure imparts unique mechanical, electrical,thermal and chemical properties to the material. Carbon nano-tubes arebelieved to have great potential for use in field emission devices,hydrogen fuel storage, rechargeable battery electrodes, coatingingredients, solid lubricant, fillers for a resin, and compositereinforcements.

Iijima was the first to report the production of carbon nanotubes by anarc discharge between two graphite rods. This technique still remains tobe the most commonly used technique for producing carbon nanotubes;however, yield of pure carbon nanotubes with respect to the end productis only about 15%. Thus, a complicated, slow and expensive purificationprocess must be carried out for particular device applications.

Kusunoki described another conventional approach to produce carbonnanotubes, which was published in an article entitled “Epitaxial CarbonNanotube Film Self-organized by Sublimation Decomposition of SiliconCarbide” (Appl. Phys. Lett. Vol. 71, pp. 2620, 1997). Carbon nanotubeswere produced at high temperatures by irradiating a laser onto graphiteor silicon carbide. In this case, the carbon nanotubes are produced fromgraphite at about 1,200° C. or more and from silicon carbide at about1,600 to 1,700° C. However, this method also requires multiple stages ofpurification which increases the cost. In addition, this method hasdifficulties in large-device applications.

Li, et al. reported a method of producing carbon nanotubes through athermal decomposition of hydrocarbon series gases by chemical vapordeposition (CVD) (“Large-Scale Synthesis of Aligned Carbon Nanotubes,”Science, Vol. 274, Dec. 6, 1996, pp. 1701-1703). This technique isapplicable only with a gas that is unstable, such as acetylene orbenzene. For example, a methane (CH₄) gas cannot be used to producecarbon nanotubes by this technique.

A carbon nanotube layer may be grown on a substrate using a plasmachemical vapor deposition method at a high density of 1011 cm⁻³ or more.The substrate may be an amorphous silicon or polysilicon substrate onwhich a catalytic metal layer is formed. In the growth of the carbonnanotube layer, a hydrocarbon series gas may be used as a plasma sourcegas, the temperature of the substrate may be in the range of 600 to 900°C., and the pressure may be in the range of 10 to 1000 mTorr.

In summary, carbon nano-tubes are extremely expensive due to the lowyield and low production and purification rates commonly associated withall of the current carbon nano-tube preparation processes. The highmaterial costs have significantly hindered the widespread application ofnano-tubes. A large number of researchers are making attempts to developmuch lower-cost processes for nano-tubes. We have taken a differentapproach in that, instead of carbon nano-tubes, we chose to developalternative nano-scaled carbon materials that exhibit comparableproperties, but are more readily available and at much lower costs.

It is envisioned that individual nano-scaled graphite planes (individualsheets of graphene plane) and clusters of multiple nano-scaled graphenesheets, collectively called “nano-sized graphene plates (NGPs),” couldprovide unique opportunities for solid state scientists to study thestructures and properties of nano carbon materials. The structures ofthese materials may be best visualized by making a longitudinal scissionon the single-wall or multi-wall of a nano-tube along its tube axisdirection and then flattening up the resulting sheet or plate (FIG. 1).Studies on the structure-property relationship in isolated NGPs couldprovide insight into the properties of a fullerene structure or carbonnano-tube. Furthermore, these nano materials could potentially becomecost-effective substitutes for carbon nano-tubes or other types ofnano-rods for various scientific and engineering applications.

Direct synthesis of the NGP material had not been possible, although thematerial had been conceptually conceived and theoretically predicted tobe capable of exhibiting many novel and useful properties. The presentinvention provides a process for producing large quantities of NGPs. Theprocess is estimated to be highly cost-effective.

SUMMARY OF THE INVENTION

As a preferred embodiment of the presently invented process, NGPs can bereadily produced by the following procedures: (1) partially or fullycarbonizing a variety of precursor polymers, such as polyacrylonitrile(PAN) fibers and phenol-formaldehyde resin, or heat-treating petroleumor coal tar pitch, (2) exfoliating the resulting carbon- orgraphite-like structure, and (3) mechanical attrition (e.g., ballmilling) of the exfoliated structure to become nano-scaled. The heattreatment temperature and time and the mechanical attrition conditionscan be varied to generate, by design, various NGP materials with a widerange of graphene plate thickness, width and length values. The heattreatment temperature typically lies in the range of 300-1,000° C. forpartial carbonization and 1,000-3,000° C. for more completecarbonization and graphitization. The processing ease and the wideproperty ranges that can be achieved with NGP materials make thempromising candidates for many important engineering applications. Theelectronic, thermal and mechanical properties of NGP materials areexpected to be comparable to those of carbon nano-tubes; but NGPs willbe available at much lower costs and in larger quantities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 conceptually illustrates the configuration difference between acarbon nano-tube and a nano-scaled graphene plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

One preferred embodiment of the present invention is a nano-scaledgraphene plate (NGP) material that is essentially composed of a sheet ofgraphite plane or a plurality of sheets of graphite plane. Each graphiteplane, also referred to as a graphene plane or basal plane, comprises atwo-dimensional hexagonal structure of carbon atoms. Each plate has alength and a width parallel to the graphite plane and a thicknessorthogonal to the graphite plane characterized in that at least one ofthe values of length, width, and thickness is 100 nanometers (nm) orsmaller. Preferably, all length, width and thickness values are smallerthan 100 nm. This NGP material can be produced by a process comprisingthe steps of: (a) carbonization or graphitization to produce a polymericcarbon, (b) exfoliation or expansion of graphite crystallites in thepolymeric carbon to delaminate or separate graphene planes, and (c)mechanical attrition of the exfoliated structure to nanometer-scaledplates.

The first step involves partially carbonizing, fully carbonizing, orgraphitizing a precursor material such as a polymer, or a petroleum orcoal tar pitch material to produce a polymeric carbon. The resultingpolymeric carbon presumably contains micron- and/or nanometer-scaledgraphite crystallites with each crystallite being composed of one sheetor several of sheets of graphite plane. Preferably, the polymeric carbonis pulverized, chopped, or milled to become small particles or shortfiber segments, with a dimension preferably smaller than 1 mm and,further preferably smaller than 0.05 mm before the second step iscarried out.

The second step involves exfoliating the graphite crystallites in thepolymeric carbon. Exfoliation typically involves a chemical treatment,intercalation, foaming, heating and/or cooling steps. The purpose of theexfoliation treatment is to delaminate (at least crack open between) thegraphene planes or to partially or fully separate graphene planes in agraphite crystallite.

The third step includes subjecting the polymeric carbon containingexfoliated graphite crystallites to a mechanical attrition treatment toproduce a nano-scaled graphene plate material. Either the individualgraphene planes (one-layer NGPs) or stacks of graphene planes bondedtogether (multi-layer NGPs) are reduced to nanometer-sized (preferablyboth length and width being smaller than 100 nm in size, furtherpreferably smaller than 10 nm in size). In the thickness direction (orc-axis direction normal to the graphene plane), there may be a smallnumber of graphene planes that are still bonded together through the vander Waal's forces that commonly hold the basal planes together in anatural graphite. Preferably, there are less than 20 layers (furtherpreferably less than 5 layers) of graphene planes, each with length andwidth smaller than 100 nm, that constitute a multi-layer NGP materialproduced after mechanical attrition. Preferred embodiments of thepresent invention are further described as follows:

Carbonization Treatment: The preparation of organic semiconductingmaterials by simple pyrolysis of polymers or petroleum/coal tar pitchmaterials has been known for approximately three decades. When polymerssuch as polyacrylonitrile (PAN), rayon, cellulose and phenolformaldehyde were heated above 300° C. in an inert atmosphere theygradually lost most of their non-carbon contents. The resultingstructure is generally referred to as a polymeric carbon. Depending uponthe heat treatment temperature (HTT) and time, polymeric carbons can bemade to be insulating, semi-conducting, or conducting with the electricconductivity range covering approximately 12 orders of magnitude. Thiswide scope of conductivity values can be further extended by doping thepolymeric carbon with electron donors or acceptors. Thesecharacteristics uniquely qualify polymeric carbons as a novel,easy-to-process class of electro-active materials whose structures andphysical properties can be readily tailor-made.

Polymeric carbons can assume an essentially amorphous structure, ahighly organized crystal (graphite), or a wide range of intermediatestructures that are characterized in that various proportions and sizesof graphite crystallites and defects are dispersed in an amorphousmatrix. Thus far, all of the earlier experimental studies on polymericcarbons have been based on bulk samples that contain a blend of graphitecrystalline structures (crystallites) of various sizes, amorphousphases, and high defect populations and, hence, the properties measuredrepresent the global properties of all the constituent phases together.No experimental work has been reported on the properties of individual,isolated carbon crystallites or graphene plates that are nanometer-sizedpresumably due to the lack of a method to directly synthesize such nanomaterials.

Polyacene (C₄H₂)_(n) and two-dimensional condensed aromatic rings orhexagons (nano-scaled graphene sheets) can be found inside themicrostructure of a heat treated polymer such as a PAN fiber. Anappreciable amount of polyacene derivatives and smaller-sized graphenesheets are believed to exist in PAN-based polymeric carbons treated at300-1,000° C. These species condense into wider aromatic ring structures(larger-sized graphene sheets) and thicker plates (more graphene sheetsstacked together) with a higher HTT or longer heat treatment time. Thesegraphene plates are gradually transformed into a well-developed“turbostratic structure” characteristic of the microstructure of acarbon fiber.

NGP materials from several classes of precursor materials were prepared.For instance, the first class includes semi-crystalline PAN in a fiberform. As compared to phenolic resin, the pyrolized PAN fiber has ahigher tendency to develop small crystallites that are dispersed in adisordered matrix. The second class, represented by phenol formaldehyde,is a more isotropic, essentially amorphous and highly cross-linkedpolymer. The third class includes petroleum and coal tar pitch materialsin bulk or fiber forms. The precursor material composition, heattreatment temperature (HTT), and heat treatment time (Htt) are threeparameters that govern the length, width, thickness (number of graphenesheets), and chemical composition of the resulting NGP materials.

PAN fibers were subjected to oxidation at 200-350° C. while under atension, and then partial or complete carbonization at 350-1,500° C. toobtain polymeric carbons with various nano-crystalline graphitestructures (graphite crystallites). Selected samples of these polymericcarbons were further heat-treated at a temperature in the range of1,500-3,000° C. to partially or fully graphitize the materials. Phenolformaldehyde resin and petroleum and coal tar pitch materials weresubjected to a similar heat treatments in a temperature range of 500 to2,500° C.

Exfoliation Treatment: In general, for the purpose of exfoliatinggraphene plane layers, the chemical treatment of pyrolyzed polymer orpitch materials involved subjecting particles of a wide range of sizes(or fibers shorter than mm in length) to a chemical solution for periodsof time ranging from about one minute to about 48 hours. The chemicalsolution was selected from a variety of oxidizing or intercalatingsolutions maintained at temperatures ranging from about room temperatureto about 125° C. The polymeric carbon particles utilized can range insize from a fine powder small enough to pass through a 325 mesh screento a size such that no dimension is greater than about one inch or 25.4mm. The concentrations of the various compounds or materials employed,e.g. H₂SO₄, HNO₃, KMnO₄, FeCL₃, etc. ranged from about 0.1 normal toconcentrated strengths. Ratios of H₂SO₄ to HNO₃ were also varied fromabout 9:1 to about 1:1 to prepare a range of acid mixtures. The chemicaltreatment may include interlayer chemical attack and/or intercalation,followed by a heating cycle. Exfoliation may also be achieved by using afoaming or blowing agent.

Interlayer chemical attack of polymeric carbon particles or short fibersis preferably achieved by subjecting the particles/fibers to oxidizingconditions. Various oxidizing agents and oxidizing mixtures may beemployed to achieve a controlled interlayer chemical attack. Forexample, there may be utilized nitric acid, potassium chlorate, chromicacid, potassium permanganate, potassium chromate, potassium dichromate,perchloric acid and the like, or mixtures such as, for instance,concentrated nitric acid and potassium chlorate, chromic acid andphosphoric acid, sulfuric acid and nitric acid, etc, or mixtures of astrong organic acid, e.g. trifluoroacetic acid and a strong oxidizingagent soluble in the organic acid used. A wide range of oxidizing agentconcentrations can be utilized. Oxidizing agent solutions havingconcentrations ranging from 0.1 normal to concentrated strengths may beeffectively employed to bring about interlayer attack. The acids or thelike utilized with the oxidizing agents to form suitable oxidizing mediaor mixtures can also be employed in concentrations ranging from about0.1 normal to concentrated strengths.

The treatment of polymeric carbon particles or fibers with oxidizingagents or oxidizing mixtures such as mentioned above is preferablycarried out at a temperature between about room temperature and about125° C. and for periods of time sufficient to produce a high degree ofinterlayer attack. The treatment time will depend upon such factors asthe temperature of the oxidizing medium, grade or type of polymericcarbon treated, particle/fiber size, amount of expansion desired andstrength of the oxidizing medium.

The opening up or splitting apart of graphene layers can also beachieved by chemically treating polymeric carbon particles/fibers withan intercalating solution or medium, hereafter referred to asintercalant, so as to insert or intercalate a suitable additive betweenthe carbon hexagon networks and thus form an addition or intercalationcompound of carbon. For example, the additive can be a halogen such asbromine or a metal halide such as ferric chloride, aluminum chloride, orthe like. A halogen, particularly bromine, may be intercalated bycontacting the polymeric carbon particles with bromine vapors or with asolution of bromine in sulfuric acid or with bromine dissolved in asuitable organic solvent. Metal halides can be intercalated bycontacting the polymeric carbon particles with a suitable metal halidesolution. For example, ferric chloride can be intercalated by contactingpolymeric carbon particles/fibers with a suitable aqueous solution offerric chloride or with a mixture comprising ferric chloride andsulfuric acid. Temperature, times, and concentrations of reactantssimilar to those mentioned earlier for oxidation treatments can also beemployed for the above intercalation processes.

Upon completion of the treatment directed to promoting interlayerattack, the thoroughly wetted or soggy polymeric carbon particles can besubjected to conditions for bringing about the expansion thereof.Preferably, however, the treated polymeric carbon particles are rinsedwith an aqueous solution. The rinsing or washing of the treatedparticles/fibers with aqueous solution may serve several functions. Forinstance, the rinsing or leaching removes harmful materials, e.g. acid,from the particles so that it can be safely handled. Moreover, it maydecompose or remove intercalated material. Furthermore, it can alsoserve as the source of the blowing or expanding agent, which is to beincorporated between layers. For example, it can serve as the source ofwater if water is to be utilized as the foaming, blowing or expandingagent.

The c-axis direction expansion is brought about by activating a materialsuch as, for example, a suitable foaming or blowing agent which has beenincorporated between layers of parallel graphene planes, theincorporation taking place either during the interlayer attack treatmentor thereafter. The incorporated foaming or blowing agent upon activationsuch as by chemical interaction or by heat generates a fluid pressure,which is effective to cause c-axis direction expansion of the polymericcarbon particles. Preferably, a foaming or blowing agent is utilizedwhich when activated forms an expanding gas or vapor which exertssufficient pressure to cause expansion.

A wide variety of well-known foaming and blowing agents can be employed.For example, there can be utilized expanding agents such as water,volatile liquids, e.g., liquid nitrogen and the like which change theirphysical state during the expansion operation. When an expanding agentof the above type is employed, the expansion of the treated polymericcarbon particles is preferably achieved by subjecting the treatedparticles to a temperature sufficient to produce a gas pressure which iseffective to bring about an almost instantaneous and maximum expansionof the particles. For instance, when the expanding agent is water, theparticles having water incorporated in the structure are preferablyrapidly heated or subjected to a temperature above 100° C. so as toinduce a substantially instantaneous and full expansion of theparticles. If such particles to be expanded are slowly heated to atemperature above 100° C., substantial water will be lost byvaporization from the structure resulting in a drying of the structureso that little expansion will be achieved. Preferably, the substantiallycomplete and full expansion of the particles is accomplished within atime of from about a fraction of a second to about 10 seconds.

In addition to physical expanding methods such as described above, theexpanding gas can be generated in situ, that is, between layers ofcarbon networks by the interaction of suitable chemical compounds or bythe use of a suitable heat sensitive additive or chemical blowing agent.

As indicated previously, the polymeric carbon particles are so treatedwith a suitable oxidizing medium and unrestrictedly expanded that thereis preferably produced expanded carbon masses having expansion ratios ofat least 20 to 1 or higher. In other words, the expanded polymericcarbon particles have a thickness or c-axis direction dimension in thegraphite crystallite at least 20 times of that of the un-expandedcrystallite. The expanded carbon particles are unitary, laminarstructure having a vermiform appearance. The vermiform masses arelightweight, anisotropic graphite-based materials.

The intercalation treatment is further described in what follows:Graphite is a crystalline form of carbon comprising hexagonally arrangedatoms bonded in flat layered planes, commonly referred to as basalplanes or graphene planes, with van der Waal's bonds between the planes.By treating particles of graphite, such as natural graphite flake, withan intercalant of e.g., a solution of sulfuric and nitric acid, thecrystal structure of the graphite reacts to form a compound of graphiteand the intercalant. The treated particles of graphite are hereafterreferred to as intercalated graphite flake. Upon exposure to elevatedtemperatures the particles of intercalated graphite expand in dimensionin an accordion-like fashion in the c-axis direction, i.e. in thedirection perpendicular to the basal planes of the graphite. In asimilar fashion, the presently heat-treated polymeric carbon, with orwithout pulverization, can be subjected to intercalation andhigh-temperature expansion treatment to obtain a polymeric carboncontaining expanded graphene planes. The polymeric carbon is typicallyintercalated by dispersing the polymeric carbon particles or shortfibers in a solution containing an oxidizing agent, such as a mixture ofnitric and sulfuric acid. After the particles or fibers are intercalatedexcess solution is drained from the particles or fibers. The quantity ofintercalation solution retained on the particles or fibers afterdraining is typically between 20 and 50 parts of solution by weight per100 parts by weight of carbon (pph). In some cases, it reaches about 100pph.

The intercalant of the present invention contains oxidizingintercalating agents known in the art of intercalated graphites. Asindicated earlier, examples include those containing oxidizing agentsand oxidizing mixtures, such as solutions containing nitric acid,potassium chlorate, chromic acid, potassium permanganate, potassiumchromate, potassium dichromate, perchloric acid, and the like, ormixtures, such as for example, concentrated nitric acid and chlorate,chromic acid and phosphoric acid, sulfuric acid and nitric acid, ormixtures of a strong organic acid, e.g. trifluoroacetic acid, and astrong oxidizing agent soluble in the organic acid.

In a preferred embodiment of the invention, the intercalant is asolution of sulfuric acid, or sulfuric acid and phosphoric acid, and anoxidizing agent, i.e. nitric acid, perchloric acid, chromic acid,potassium permanganate, iodic or periodic acids, or the like, andpreferably also includes an expansion aid as described below. Theintercalant may contain metal halides such as ferric chloride, andferric chloride mixed with sulfuric acid, or a halogen, such as bromineas a solution of bromine and sulfuric acid or bromine in an organicsolvent.

The polymeric carbon particles or fibers treated with intercalant arecontacted e.g. by blending, with a reducing organic agent selected fromalcohols, sugars, aldehydes and esters which are reactive with thesurface film of oxidizing intercalating solution at temperatures in therange of 25° C. and 125° C. Suitable specific organic agents include thefollowing: hexadecanol, octadecanol, 1-octanol, 2-octanol, decylalcohol,1,10 decanediol, decylaldehyde, 1-propanol, 1,3 propanediol,ethyleneglycol, polypropylene glycol, dextrose, fructose, lactose,sucrose, potato starch, ethylene glycol monostearate, diethylene glycoldibenzoate, propylene glycol monostearate, propylene glycol monooleate,glycerol monostearate, glycerol monooleate, dimethyl oxylate, diethyloxylate, methyl formate, ethyl formate and ascorbic acid. Depending uponthe chemicals used in the exfoliation treatment, the edge of a grapheneplane may contain some non-carbon atoms such as hydrogen, oxygen,nitrogen, sulphur, and combinations thereof.

Mechanical Attrition: The exfoliated particles or short fiber segmentswere then submitted to a mechanical attrition treatment to furtherseparate graphene planes and reduce the sizes of particles or fibers tobe nanometer-scaled. Attrition can be achieved by pulverization,grinding, milling, etc., but the most effective method of attrition isball-milling. High-energy planetary ball mills were found to beparticularly effective in producing nano-scaled graphene plates. Since,ball milling is considered to be a mass production process, thepresently invented process is capable of producing large quantities ofNGP materials cost-effectively. This is in sharp contrast to theproduction and purification processes of carbon nano-tubes, which areslow and expensive.

The nano-scaled graphene plate (NGP) material produced by the presentlyinvented process can be readily incorporated in a matrix material toobtain an NGP-reinforced composite. The matrix material can be selectedfrom a polymer (both thermoset and thermoplastic), organic, ceramic,glass, carbon, metal, or a combination thereof. The NGP-reinforcedcomposites exhibit desirable mechanical and physical properties. In somecases (e.g., polymer matrix), either the strength or the failure strainwas improved, with a concomitant increase in electrical and thermalconductivities. In other cases (e.g., ceramic matrix), the fracturetoughness was improved over the corresponding un-reinforced matrixmaterial. Typically, an NGP proportion of approximately 15 volumepercent was sufficient to produce significantly improved properties. Inmany cases, an addition of NGPs in the amount of 1%-5% by volume wasadequate.

EXAMPLE 1

One hundred grams of polymeric carbon, prepared by oxidation of PANfibers at 250° C. and partial carbonization of the oxidized PAN at 500°C., were treated in a mixture of sulfuric and nitric acids atconcentrations to yield the desired intercalation compound. The productwas water washed and dried to approximately 1% by weight water. Thedried fibers were introduced into a furnace at 1,250° C. to effectextremely rapid and high expansions of nano-scaled graphitecrystallites. The exfoliated carbon sample, chopped into a short fiberform (<1 mm length), was then ball-milled in a high-energy plenary ballmill machine for 24 hours to produce nano-scaled particles.

EXAMPLE 2

Same as in Example 1, but the carbonization temperature was 1,000° C.

EXAMPLE 3

A phenol formaldehyde resin was heat treated in an inert atmosphere at aHTT in the range of 350-900° C. to obtain polymeric carbon, which wasground to mm-sized particles and then subjected to solution treatmentsto obtain exfoliated polymeric carbons. Samples containing exfoliatedgraphite crystallites were then ball-milled to become nanometer-sizedpowder.

EXAMPLE 4

A coal tar pitch sample was heat treated in an inert atmosphere at a HTTin the range of 350-900° C. to obtain polymeric carbon, which wasfurther heat-treated at 2,500° C. and ground to mm-sized particles andthen subjected to solution treatments to obtain exfoliated polymericcarbons. Specifically, 25 grams of the polymeric carbon particles wereintercalated with twenty-five grams of intercalant consisting of 86parts by weight of 93% sulfuric acid and 14 parts by weight of 67%nitric acid. The particles were then placed in a 90° C. oven for 20minutes. The intercalated particles were then washed with water. Aftereach washing the particles were filtered by vacuum through a Teflonscreen. After the final wash the particles were dried for 1 hour in a115° C. oven. The dried particles were then rapidly heated toapproximately 1000° C. to further promote expansion. Samples containingexfoliated graphite crystallites were then ball-milled to becomenanometer-sized powder.

EXAMPLE 5

A petroleum pitch sample was heat treated in an inert atmosphere at aHTT of 350° C. and extruded into a polymeric carbon fiber, which wasfurther heat-treated at 2,500° C. and ground to mm-sized particles andthen subjected to solution treatments to obtain exfoliated polymericcarbons. Specifically, 25 grams of the polymeric carbon particles wereintercalated with twenty-five grams of intercalant consisting of 86parts by weight of 93% sulfuric acid and 14 parts by weight of 67%nitric acid. After mixing for three minutes, 1.0 grams of decanol wereblended into the particles. The particles were then placed in a 90° C.oven for 20 minutes. The intercalated particles were then washed withwater. After each washing the particles were filtered by vacuum througha Teflon screen. After the final wash the particles were dried for 1hour in a 115° C. oven. The dried particles were then rapidly heated toapproximately 1,000° C. to further promote expansion. Samples containingexfoliated graphite crystallites were then ball-milled to becomenanometer-sized powder.

EXAMPLE 6

The nanometer-sized powder obtained in EXAMPLE 5 was mixed with epoxyresin (Epon 828 and Z curing agent at a 4:1 ratio) to obtain anano-scaled graphene plate (NGP) reinforced epoxy composite. A 35%increase in three-point-bending strength over the un-reinforced epoxywas observed with a composite containing only a 5% by volume of NGPs.

EXAMPLE 7

The nanometer-sized powder obtained in EXAMPLE 4 was mixed withpolymethylmethacrylate (PMMA) to obtain an NGP-reinforced PMMAcomposite. An increase in tensile failure strain from approximately 5%for the un-reinforced PMMA to approximately 18% for an NGP(5%)-PMMAcomposite.

1-5. (canceled)
 6. A process for producing a nano-scaled graphene platematerial comprising the steps of: a). either partially or fullycarbonizing a precursor polymer or heat-treating petroleum or coal tarpitch to produce a polymeric carbon containing micron- and/ornanometer-scaled graphite crystallites with each crystallite comprisingone sheet or a multiplicity of sheets of graphite plane; b). exfoliatingsaid graphite crystallites in said polymeric carbon; and c). subjectingsaid polymeric carbon containing exfoliated graphite crystallites to amechanical attrition treatment to produce said nano-scaled grapheneplate material.
 7. The process for producing nano-scaled graphene platematerial as defined in claim 6, wherein said precursor polymer,petroleum or coal tar pitch is in a fiber form.
 8. The process forproducing nano-scaled graphene plate material as defined in claim 6,wherein said precursor polymer is selected from the group consisting ofpolyacrylonitrile and its copolymers or derivatives, phenol formaldehydeand its copolymers or derivatives, rayon and its derivatives, celluloseand its derivatives, and combinations thereof.
 9. The process forproducing nano-scaled graphene plate material as defined in claim 6,wherein said step of carbonizing or heat-treating comprises a heattreatment at a temperature in the range of 300° C. to 2,500° C.
 10. Theprocess for producing nano-scaled graphene plate material as defined inclaim 6, wherein said step of carbonizing or heat-treating comprises aheat treatment at a temperature in the range of 300° C. to 1,000° C. 11.The process for producing nano-scaled graphene plate material as definedin claim 6, wherein said step of exfoliating comprises a chemicaltreatment that includes an interlayer chemical attack, intercalation,foaming, heating and/or cooling.
 12. The process for producingnano-scaled graphene plate material as defined in claim 6, wherein saidstep of exfoliating comprises contacting said polymeric carbon with anoxidizing agent selected from the group consisting of nitric acid,potassium chlorate, chromic acid, potassium permanganate, potassiumchromate, potassium dichromate, perchloric acid, phosphoric acid,sulfuric acid, trifluoroacetic acid, organic acid, and mixtures thereof.13. The process for producing nano-scaled graphene plate material asdefined in claim 6, wherein said mechanical attrition treatmentcomprises a ball milling treatment of said polymeric carbon.
 14. Theprocess for producing nano-scaled graphene plate material as defined inclaim 6, wherein said mechanical attrition treatment comprises operatinga high-energy planetary ball mill.
 15. The process for producingnano-scaled graphene plate material as defined in claim 6, wherein saidpolymeric carbon produced in step (a) is pulverized to become smallparticle or short fiber segment forms prior to step (b). 16-19.(canceled)